An aqueous electrolyte for a zinc-sulfur battery, a preparation method thereof, and an application thereof

Abstract

The present invention belongs to the technical field of batteries and relates to an aqueous electrolyte for a zinc-sulfur battery, a preparation method thereof, and an application. The aqueous electrolyte includes a zinc salt, a phosphomolybdate, N-formylpiperidine, and water; in the aqueous electrolyte, the mass fraction of the phosphomolybdate is 0.01 to 0.2% w / w, and the volume fraction of N-formylpiperidine is 5 to 20% v / v. By adding a phosphomolybdate and N-formylpiperidine as electrolyte additives to the aqueous electrolyte of the zinc-sulfur battery, the present invention can achieve synergistic regulation of the positive and negative electrodes, and is expected to realize the preparation of an aqueous zinc-sulfur battery with high electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to an aqueous electrolyte for a zinc-sulfur battery, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the global economy and the continuous growth of the population, the global energy demand shows an increasing trend. Lithium-ion batteries have become the main force in the energy storage market due to their significant characteristics such as green cleanliness and stable cycling. However, the further development of lithium-ion batteries faces severe challenges: the reserves of lithium resources on the earth are extremely unevenly distributed, mainly concentrated in a few countries and regions; moreover, with the continuous expansion of the lithium-ion battery market, the demand for lithium resources is increasing day by day, resulting in the increasing scarcity and high price of lithium resources. The limited nature of this resource and the high price seriously restrict the wide application of lithium-ion batteries in the field of large-scale energy storage.

[0003] In contrast, aqueous zinc-ion batteries (AZIBs) have shown many advantages as potential alternative technologies in the field of large-scale energy storage due to their abundant resources, low cost, high safety, and environmental friendliness. Among the existing cathode materials developed and applied in AZIBs, such as manganese-based compounds, vanadium-based compounds, Prussian blue, and organic compounds, there are problems of relatively low theoretical specific capacity, and their values are all less than 400 mAh / g. This relatively low theoretical specific capacity limits the energy density of the battery and cannot meet the urgent market demand for high-energy-density batteries. Especially in aspects such as long driving ranges of electric vehicles and high energy storage capacities of large-scale energy storage power stations, the limitations of these traditional cathode materials become more obvious. In contrast, sulfur cathode materials based on conversion reactions stand out and have many significant advantages. First, from an electrochemical perspective, sulfur cathodes benefit from a two-electron transfer mechanism during the reaction and have an extremely high theoretical capacity, approximately 1675 mAh / g. A high theoretical capacity means that the battery can store more electrical energy under the same mass or volume, thus significantly increasing the energy density of the battery and meeting the market demand for high-energy-density batteries. Second, from the perspectives of cost and environmental protection, sulfur elements are abundant in nature, have a wide source, and are relatively inexpensive, which makes sulfur cathode materials have obvious cost advantages in large-scale applications. At the same time, sulfur itself is safe and non-toxic, and is environmentally friendly during production and use, and will not cause environmental problems such as heavy metal pollution.

[0004] Although zinc-sulfur batteries have great potential in terms of being green, low-cost, and having high energy density, there are still many problems to be solved in current aqueous zinc-sulfur batteries. On the positive electrode side, the conversion reaction kinetics of the sulfur positive electrode are slow. This limits the electrode reaction rate during the charge and discharge process of the battery, resulting in a low charge and discharge efficiency of the battery, inability to achieve fast charge and discharge, and seriously affecting the actual application performance of the battery. On the zinc negative electrode side, the hydrogen evolution side reaction is relatively serious. During the charge and discharge process of the battery, water is reduced on the surface of the negative electrode to generate hydrogen. This not only consumes the water in the electrolyte and reduces the Coulomb efficiency of the battery, but may also cause an increase in the internal pressure of the battery, leading to safety problems. In addition, there is also the problem of dendrite growth on the zinc negative electrode during the cycling process. As the number of charge and discharge cycles increases, zinc dendrites gradually grow and may pierce the separator, causing the battery to short-circuit, greatly shortening the cycle life and safety of the battery. These problems seriously hinder the commercialization process of aqueous zinc-sulfur batteries. Therefore, it is urgent to further develop aqueous zinc-sulfur batteries by regulating the positive and negative electrodes. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the purpose of the present invention is to provide an aqueous electrolyte for a zinc-sulfur battery, its preparation method and application, so as to overcome the deficiencies of the prior art.

[0006] One object of the present invention is achieved through the following technical solutions:

[0007] An aqueous electrolyte for a zinc-sulfur battery, comprising a zinc salt, a phosphomolybdate, N-formylpiperidine, and water; in the aqueous electrolyte, the mass fraction of the phosphomolybdate is 0.01 - 0.2% w / w, and the volume fraction of N-formylpiperidine is 5 - 20% v / v.

[0008] Preferably, the zinc salt is zinc trifluoromethanesulfonate and / or zinc sulfate.

[0009] Preferably, the phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate, and potassium phosphomolybdate.

[0010] Preferably, in the aqueous electrolyte, the concentration of the zinc salt is 0.5 - 5 mol / L.

[0011] Preferably, the mass fraction of the phosphomolybdate is 0.03 - 0.1% w / w.

[0012] Preferably, the volume fraction of N-formylpiperidine is 8 - 15% v / v.

[0013] The second object of the present invention is achieved through the following technical solutions:

[0014] A preparation method for an aqueous electrolyte of a zinc-sulfur battery, comprising the following steps:

[0015] Dissolve the zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; sequentially add the phosphomolybdate and N-formylpiperidine to the mixed solution and stir evenly to obtain an aqueous electrolyte.

[0016] The third object of the present invention is achieved by the following technical solution:

[0017] An aqueous zinc-sulfur battery includes a positive electrode material, a negative electrode material, a separator, and the above-mentioned aqueous electrolyte.

[0018] Preferably, the positive electrode material includes a positive electrode active material, a conductive agent, and a binder. Among them, the positive electrode active material includes sulfur or sulfur-carbon, etc.

[0019] Preferably, the negative electrode material is zinc foil.

[0020] The fourth object of the present invention is achieved by the following technical solution:

[0021] A preparation method of an aqueous zinc-sulfur battery includes the following steps:

[0022] Mix and grind the positive electrode materials evenly, coat them on the current collector, and dry to obtain a positive electrode sheet;

[0023] Dissolve the zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; sequentially add the phosphomolybdate and N-formylpiperidine to the mixed solution and stir evenly to obtain an aqueous electrolyte;

[0024] Assemble the positive electrode sheet, zinc metal, aqueous electrolyte, and separator into a battery.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. In the aqueous electrolyte of the zinc-sulfur battery of the present invention, adding phosphomolybdate and N-formylpiperidine as electrolyte additives can achieve the synergistic regulation of the positive and negative electrodes. Among them, on the positive electrode, the phosphomolybdate reduces the conversion energy barrier and promotes the conversion reaction; on the negative electrode, N-formylpiperidine can promote the uniform deposition of Zn 2+ and inhibit dendrite growth. Therefore, this synergistic regulation strategy is expected to realize an aqueous zinc-sulfur battery with high electrochemical performance.

[0027] 2. The zinc-sulfur battery prepared with the electrolyte of the present invention has excellent electrochemical performance. At a current density of 0.5 A / g, the specific capacity of the battery can reach more than 1480 mAh / g. At a current density of 5 A / g, after 300 cycles, the battery can still maintain more than 70% of its capacity.

[0028] 3. By changing the electrolyte composition, the present invention is expected to improve the electrochemical performance of the aqueous zinc-sulfur battery, achieve the preparation of a higher-performance aqueous zinc-sulfur battery, and expand its application scope in large-scale energy storage, electric vehicles, and portable devices. Detailed Embodiments

[0029] Hereinafter, embodiments of the aqueous electrolyte of the zinc-sulfur battery of the present invention, its preparation method, and applications will be described in detail. However, these embodiments are exemplary, and the disclosure of the present invention is not limited thereto.

[0030] The aqueous electrolyte of the zinc-sulfur battery provided in some embodiments of the present invention includes a zinc salt, a phosphomolybdate, N-formylpiperidine, and water.

[0031] In the present invention, by adding a phosphomolybdate and N-formylpiperidine as electrolyte additives to the aqueous electrolyte of the zinc-sulfur battery, the conductivity of the electrolyte is improved, the contact resistance between the electrode and the electrolyte is reduced, and the cycle stability of the zinc-sulfur battery at a high current density is improved. Specifically, the phosphomolybdate can specifically bind to the active substance, can act as a catalyst to reduce the activation energy barrier of the active substance conversion, and inhibit the generation of by-products, thereby improving the conversion kinetics and cycle reversibility of the sulfur cathode. And N-formylpiperidine, as an organic compound, the oxygen atom in its molecule is expected to be affinity for the surface of the zinc metal anode, thereby forming a hydrophobic solid electrolyte interface film. With the protection of this film, the contact with active water molecules on the zinc metal anode can be reduced, and the occurrence of the hydrogen evolution reaction is inhibited. Secondly, N-formylpiperidine is expected to participate in the Zn 2+ solvation structure, replacing some water molecules in the solvation shell, and the regulated solvation structure guides Zn 2+ to deposit uniformly on the anode, thereby inhibiting the growth of anode dendrites.

[0032] Preferably, in the aqueous electrolyte, the mass fraction of the phosphomolybdate is 0.01 - 0.2% w / w. If the addition amount of the phosphomolybdate is too small, there will be no significant effect. On the one hand, adding too much increases the cost, and on the other hand, it will also cause some side reactions, which will instead reduce the capacity retention of the battery. The mass fraction of the phosphomolybdate is further preferably 0.03 - 0.1% w / w, and can be any value among 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 mol / L, for example.

[0033] Preferably, in the aqueous electrolyte, the volume fraction of N-formylpiperidine is 5-20% v / v. Adding too much N-formylpiperidine may excessively change the composition and structure of the solvation sheath, which will instead reduce the battery capacity and cycle life. The volume fraction of N-formylpiperidine is further preferably 8-15% v / v, and can be any value among 8, 9, 10, 11, 12, 13, 14, 15% v / v, for example.

[0034] Preferably, in the aqueous electrolyte, the concentration of zinc salt is 0.5-5 mol / L; more preferably 1-3 mol / L. It can be any value among 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.7, 3 mol / L, for example.

[0035] Preferably, the zinc salt is zinc trifluoromethanesulfonate (Zn(CF 3 SO 3 ) 2 ) and / or zinc sulfate. Preferably, the phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate, and potassium phosphomolybdate.

[0036] In some embodiments of the present invention, the provided aqueous zinc-sulfur battery includes a positive electrode material, a negative electrode material, a separator, and the above-mentioned aqueous electrolyte.

[0037] Preferably, the positive electrode material includes a positive electrode active material, a conductive agent, and a binder. Among them, the positive electrode active material includes sulfur or sulfur-carbon, etc. Sulfur-carbon is a composite of sulfur and a carbon material.

[0038] The conductive agent is not particularly limited, and any conductive agent that can be used in a battery can be used, and can be listed as one or several of activated carbon, carbon nanotubes, acetylene black, and graphite. The binder is also not particularly limited, and any binder that can be used in a battery can be used, and can be listed as one or several of polyvinylidene fluoride (PVDF), styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), and polytetrafluoroethylene (PTFE).

[0039] In the positive electrode material, the mass fractions of the positive electrode active material, the conductive agent, and the binder are 60-90%, 5-20%, and 5-20% respectively.

[0040] Preferably, the negative electrode material is zinc foil.

[0041] Preferably, the separator is a polyethylene separator, a polypropylene separator, or glass fiber, etc.

[0042] In some embodiments of the present invention, the preparation method of the provided aqueous zinc-sulfur battery includes the following steps:

[0043] Mix the cathode material evenly by grinding, coat it on the current collector, and dry it to obtain the cathode sheet;

[0044] Dissolve the zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; sequentially add the phosphomolybdate and N-formylpiperidine to the mixed solution and stir evenly to obtain an aqueous electrolyte;

[0045] Assemble the cathode sheet, zinc metal, aqueous electrolyte and separator into a battery.

[0046] Preferably, the current collector is one of carbon paper, carbon cloth, nickel foam, metal foil, etc.

[0047] The technical solution of the present invention will be further described and illustrated below through specific examples. It should be understood that the specific examples described here are only used to help understand the present invention and are not used for specific limitations of the present invention. If there is no special description, the raw materials used in the examples of the present invention are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0048] The potassium phosphomolybdate used in the following examples and comparative examples was self-made, and the steps were as follows: dissolve phosphomolybdic acid in water to form a 3 mg / mL phosphomolybdic acid solution; weigh KCl and dissolve it in water to form a 6 mg / mL KCl solution; add an equal volume of the phosphomolybdic acid solution to the KCl solution and stir evenly; then transfer the mixed solution to a hydrothermal reaction kettle, react at 100 °C for 10 h, and finally collect by centrifugal washing with deionized water and ethanol and dry to obtain potassium phosphomolybdate.

[0049] Example 1

[0050] The aqueous electrolyte provided in this example consists of Zn(CF 3 SO 3 ) 2 , potassium phosphomolybdate, N-formylpiperidine, and water, wherein the concentration of Zn(CF 3 SO 3 ) 2 is 2 mol / L, the mass fraction of potassium phosphomolybdate is 0.05% w / w, and the volume fraction of N-formylpiperidine is 10% v / v.

[0051] Weigh each raw material according to the raw material addition amount, and then dissolve Zn(CF 3 SO 3 ) 2 in water, and continuously stir at 400 rpm with a magnetic stirrer at room temperature until the solution is completely clear, transparent and free of precipitation to obtain a mixed solution; sequentially add potassium phosphomolybdate and N-formylpiperidine to the mixed solution, and continuously stir under a magnetic stirrer until the electrolyte additives are completely dissolved to obtain the aqueous electrolyte.

[0052] Example 2

[0053] The difference between Example 2 and Example 1 is that the mass fraction of potassium phosphomolybdate in Example 2 is 0.03% w / w, and the others are the same as in Example 1.

[0054] Example 3

[0055] The difference between Example 3 and Example 1 is that the mass fraction of potassium phosphomolybdate in Example 3 is 0.08% w / w, and the others are the same as in Example 1.

[0056] Example 4

[0057] The difference between Example 4 and Example 1 is that the volume fraction of N-formylpiperidine in Example 4 is 8% v / v, and the others are the same as in Example 1.

[0058] Example 5

[0059] The difference between Example 5 and Example 1 is that the volume fraction of N-formylpiperidine in Example 5 is 15% v / v, and the others are the same as in Example 1.

[0060] Example 6

[0061] The aqueous electrolyte provided in this example is composed of zinc sulfate, potassium phosphomolybdate, N-formylpiperidine, and water, wherein the concentration of zinc sulfate is 3 mol / L, the mass fraction of potassium phosphomolybdate is 0.07% w / w, and the volume fraction of N-formylpiperidine is 12% v / v.

[0062] The preparation method of the aqueous electrolyte is the same as that in Example 1.

[0063] Comparative Example 1

[0064] The aqueous electrolyte of Comparative Example 1 consists of Zn(CF 3 SO 3 ) 2 and water, wherein the concentration of Zn(CF 3 SO 3 ) 2 is 2 mol / L.

[0065] Dissolve Zn(CF 3 SO 3 ) 2 in water, and use a magnetic stirrer to stir continuously at 400 rpm at room temperature until the solution is completely clear, transparent and free of precipitation to obtain the aqueous electrolyte.

[0066] Comparative Example 2

[0067] The aqueous electrolyte of Comparative Example 2 consists of Zn(CF 3 SO 3 ) 2, N-formylpiperidine, and water, where the concentration of Zn(CF 3 SO 3 ) 2 is 2 mol / L and the volume fraction of N-formylpiperidine is 10% v / v.

[0068] Weigh each raw material according to the raw material addition amount, and then dissolve Zn(CF 3 SO 3 ) 2 in water. Use a magnetic stirrer to continuously stir at 400 rpm at room temperature until the solution is completely clear, transparent, and free of precipitation to obtain a mixed solution; add N-formylpiperidine to the mixed solution and continuously stir under the magnetic stirrer until the electrolyte additive is completely dissolved to obtain an aqueous electrolyte.

[0069] Comparative Example 3

[0070] The aqueous electrolyte of Comparative Example 3 consists of Zn(CF 3 SO 3 ) 2 , potassium phosphomolybdate, and water, where the concentration of Zn(CF 3 SO 3 ) 2 is 2 mol / L and the mass fraction of potassium phosphomolybdate is 0.05% w / w.

[0071] Weigh each raw material according to the raw material addition amount, and then dissolve Zn(CF 3 SO 3 ) 2 in water. Use a magnetic stirrer to continuously stir at 400 rpm at room temperature until the solution is completely clear, transparent, and free of precipitation to obtain a mixed solution; add potassium phosphomolybdate to the mixed solution and continuously stir under the magnetic stirrer until the electrolyte additive is completely dissolved to obtain an aqueous electrolyte.

[0072] Comparative Example 4

[0073] The difference between Comparative Example 4 and Example 1 is that the mass fraction of potassium phosphomolybdate in Comparative Example 4 is 0.3% w / w, and the others are the same as in Example 1.

[0074] Comparative Example 5

[0075] The difference between Comparative Example 5 and Example 1 is that the volume fraction of N-formylpiperidine in Comparative Example 5 is 30% v / v, and the others are the same as in Example 1.

[0076] Assemble batteries using the electrolytes of Examples 1-6 and Comparative Examples 1-5. The specific steps are as follows:

[0077] (1) 50% sulfur carbon powder, acetylene black and polyvinylidene fluoride are uniformly mixed in a mass ratio of 8:1:1, alcohol is added, and the mixture is fully ground and stirred to obtain a positive electrode slurry, and the slurry is scraped onto carbon paper, dried and baked to obtain a positive electrode sheet;

[0078] (2) Assemble the positive electrode, zinc metal, aqueous electrolyte and separator glass fiber into a button battery.

[0079] The button cells composed of the electrolytes of Examples 1-6 and Comparative Examples 1-5 are marked as button cells 1-11, respectively.

[0080] The above battery was subjected to constant current charge and discharge test, and its specific capacity was measured at a current density of 0.5 A / g; the cycle capacity retention rate was tested after 300 cycles at a current density of 5 A / g; the experimental results are shown in Table 1:

[0081] Table 1 Capacity and cycle stability of button batteries 1-11

[0082]

[0083] As can be seen from Table 1, the cycle stability of battery 7 is poor when using an electrolyte composed only of zinc salts, and a single zinc salt electrolyte cannot provide sufficient electrochemical stability. When using an electrolyte composed only of N-formylpiperidine as an additive, the capacity retention rate of battery 8 after 300 cycles is very low, which shows that the addition of N-formylpiperidine alone does not improve the battery cycle performance much; when using an electrolyte composed only of phosphomolybdate as an additive, the capacity retention rate of battery 9 is low, indicating that although the addition of a single phosphomolybdate has a certain improvement on the battery performance, the effect is very limited. The battery assembled using the electrolyte of Examples 1-6 shows excellent specific capacity and cycle stability, and the capacity retention rate still reaches more than 70% after 300 cycles at a current density of 5A / g.

[0084] It can be seen from the experimental data of button batteries 1, 10, and 11 that when the amount of phosphomolybdate and N-formylpiperidine added to the electrolyte is too much, the capacity and capacity retention rate of the battery will be reduced.

[0085] The various aspects, embodiments, and features of the present invention should be considered to be illustrative in all aspects and not limiting of the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.

[0086] In the preparation method of the present invention, the order of each step is not limited to the listed order. For those of ordinary skill in the art, without creative efforts, the changes in the sequence of each step are also within the protection scope of the present invention. In addition, two or more steps or actions can be carried out simultaneously.

[0087] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and do not limit the implementation manners of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. It is not necessary and impossible to list all implementation manners here. And these obvious changes or variations derived from the essence of the present invention still fall within the protection scope of the present invention. Interpreting them as any additional restrictions is contrary to the spirit of the present invention.

Claims

1. An aqueous electrolyte for a zinc-sulfur battery, characterized in that: The invention comprises zinc salt, phosphomolybdic acid salt, N-formylpiperidine and water; in the aqueous electrolyte, the mass fraction of phosphomolybdic acid salt is 0.01-0.2% w / w, and the volume fraction of N-formylpiperidine is 5-20% v / v.

2. The aqueous electrolyte according to claim 1, characterized in that The zinc salt is zinc trifluoromethanesulfonate and / or zinc sulfate.

3. The aqueous electrolyte according to claim 1, characterized in that The phosphomolybdate is one or more of ammonium phosphomolybdate, sodium phosphomolybdate and potassium phosphomolybdate.

4. The aqueous electrolyte according to claim 1, characterized in that In the aqueous electrolyte, the concentration of zinc salt is 0.5-5 mol / L.

5. The aqueous electrolyte according to claim 1, characterized in that: The mass fraction of phosphomolybdate is 0.03~0.1%w / w.

6. The aqueous electrolyte according to claim 1, characterized in that The volume fraction of N-formylpiperidine is 8-15% v / v.

7. The method for preparing an aqueous electrolyte for a zinc-sulfur battery according to claim 1, characterized in that: The following steps are involved: Dissolve zinc salt in water and stir until the zinc salt is dissolved to obtain a mixed solution; add phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stir evenly to obtain an aqueous electrolyte.

8. An aqueous zinc-sulfur battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a separator and the aqueous electrolyte as claimed in claim 1.

9. The aqueous zinc-sulfur battery according to claim 8, characterized in that: The positive electrode material comprises a positive electrode active material, a conductive agent and a binder, and the positive electrode active material comprises sulfur or sulfur carbon; The negative electrode material is zinc foil.

10. The method for preparing an aqueous zinc-sulfur battery according to claim 8, characterized in that: The following steps are involved: The positive electrode materials are mixed and ground evenly, coated on a current collector, and dried to obtain a positive electrode sheet; Dissolving zinc salt in water and stirring until the zinc salt is dissolved to obtain a mixed solution; adding phosphomolybdate and N-formylpiperidine to the mixed solution in sequence and stirring evenly to obtain an aqueous electrolyte; The positive electrode sheet, zinc metal, aqueous electrolyte and separator are assembled into a battery.

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